This invention relates to a brake assembly, and more particularly, the invention relates to a method and apparatus of piloting a brake drum onto a hub assembly.
A brake drum is mounted onto a hub assembly for receiving a braking force applied to the brake drum by brake shoes. The brake drum must be properly positioned relative to the hub assembly, which is commonly referred to as piloting, so that the axis of the brake drum is concentric with the axis of the hub assembly and the drum and hub assembly are fully seated against one another. Ensuring concentricity between the brake drum and hub assembly is critical in order to prevent a catastrophic failure resulting from vibrations induced by a misaligned brake drum. For one type of brake assembly configuration, the large central opening of the brake drum is piloted on the barrel portion of the hub assembly to align the brake drum with the hub assembly. In another type of configuration typically used in transit bus applications, the brake drum is piloted on the outer circumference of the hub flange, which includes the studs used to secure the brake drum to the hub assembly. The brake drum pilot includes a pilot surface that extends circumferentially 360xc2x0 along an inner face of the annular mounting portion of the brake drum, which defines the central opening.
The outer circumference of the hub flange must have a relatively tight tolerance for cylindricity since the pilot surface engages the outer circumference to locate the brake drum relative to the hub assembly. If the diameter of the hub flange is too large in any area, then the drum will not seat properly and the drum and hub assembly may not be concentric. The studs are pressed into holes in the hub flange and may result in the outer circumference of the flange deforming the flange so it is enlarged in areas. As a result, the brake drum may not properly pilot onto the hub flange so that the brake drum is not concentric with the hub assembly and/or the mounting portion of the brake drum is not seated flush against the face of the hub flange, which may generate vibrations resulting in a catastrophic failure. To this end, the outer circumference of the hub flange is machined after the studs are pressed into the flange. However, when the hubs are serviced in the field with new studs, the flange may swell again deforming the outer circumference of the hub flange so that it is enlarged. Therefore, what is needed is a drum pilot and method that ensures that the brake drum properly pilots onto the hub assembly without requiring costly machining operations.
The present invention provides a brake assembly including a hub assembly having a barrel portion and a flange extending radially outwardly from the barrel portion. The flange includes an outer circumference, and a plurality of studs are arranged circumferentially about the flange extending axially there from inboard of the outer circumference. A brake drum includes a generally annular mounting portion and includes a plurality of mounting holes spaced circumferentially thereabout with the plurality of studs disposed within the plurality of mounting holes. A generally cylindrical brake flange extends axially from the mounting portion in a direction away from the barrel portion. A pilot extends axially from the mounting portion in the same direction as the cylindrical brake flange. The pilot is arranged circumferentially about the mounting portion and defines a pilot surface engaging the outer circumference of the hub flange. The pilot includes a plurality of relief pockets aligned with the plurality of studs interrupting the pilot surface such that the pilot surfaces are spaced from one another. Installation of the studs into the hub flange generates a deformed area in the outer circumference of the hub flange that is generally aligned with the stud. The deformed areas are received in the relief pockets so that deformation of the outer circumference of the hub flange does not interfere with properly piloting of the brake drum onto the hub assembly.
Accordingly, the above provides a drum pilot and method that ensures that the brake drum properly pilots onto the hub assembly without requiring costly machining operations.